Lithographic apparatus and a device manufacturing method

ABSTRACT

A lithographic apparatus is disclosed. The apparatus includes a support constructed to support a patterning device, the patterning device being capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam. A projection system is configured to project the patterned radiation beam onto a target portion of a substrate. A first vacuum environment contains the projection system, a second vacuum environment contains the patterning device support, and a separator separates the first and second vacuum environments. The separator includes an aperture for passing the projection beam from the first vacuum environment towards the patterning device and/or vice-versa. The patterning device forms at least part of a seal for substantially sealing the aperture of the separator.

FIELD

The present invention relates to a lithographic apparatus, a method formanufacturing a device, and a device manufactured thereby.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

U.S. Pat. No. 6,333,775, which is incorporated herein by reference,describes a lithographic apparatus, including multiple pressure zonesfor controlling particle contamination on the reticle and carboncontamination of optical surfaces of optical surfaces. The known systemincludes a vacuum apparatus that includes various compartments that aremaintained at different pressures. One of the compartments is a reticlezone which encases a reticle stage. Below the reticle zone, an opticszone is provided which encases projection optics devices. A reticlemetrology tray separates the reticle zone from the optics zone. Thereticle zone is maintained at a vacuum pressure of less than about 100mTorr and preferably at about 30 mTorr. The optics zone is maintained ata vacuum pressure of less than about 5 mTorr. A seal assembly provides agas limiting seal at the outer perimeter of the reticle metrology tray.The center of the reticle metrology tray includes an aperture throughwhich light beams enter and exit. During use, about 200 L/s (litres persecond) gas flows through this aperture from the reticle zone into theoptics zone.

In the known apparatus, the reticle stage is kept in a reticle zone,partially separated from the projection optics. Therefore, the volume ofthe optics zone can be relatively small, including a relatively smallnumber of components, compared to an apparatus wherein the reticle stageand the projection optics are located in the same vacuum environment.Consequently, the optics zone can be pumped down to a desired vacuumlevel relatively fast.

A disadvantage of the known lithography apparatus is that a relativelylarge amount of contamination can still reach the optics zone from thereticle zone via the aperture. Such contamination, for example, smallparticles, hydrocarbon and/or water, may hamper the operation of theoptics, as well as spoil the optics as such. This hinders a respectivedevice manufacturing method, leading to relatively expensive and/orlow-quality devices manufactured thereby.

SUMMARY

It is an aspect of the invention to provide a lithographic system inwhich contamination of the projection optics may be prevented.

It is an aspect of the invention to provide a lithographic manufacturingmethod in which contamination of the projection optics may be prevented.

It is an aspect of the invention to provide relatively inexpensiveand/or high quality devices manufactured by a lithographic apparatusand/or by a lithographic manufacturing method.

According to an aspect of the invention, a lithographic apparatusincludes a support constructed to support a patterning device. Thepatterning device is capable of imparting a radiation beam with apattern in its cross-section to form a patterned radiation beam. Theapparatus also includes a projection system configured to project thepatterned radiation beam onto a target portion of a substrate, a firstvacuum environment containing the projection system, a second vacuumenvironment containing the patterning device support, and a separatorseparating the first vacuum environment and the second vacuumenvironment. The separator includes an aperture for passing theprojection beam from the first vacuum environment towards the patterningdevice and/or vice-versa. The patterning device forms at least part of aseal for substantially sealing the aperture of the separator.

Therefore, contamination of the projection system may be preventedrelatively well, leading to lower system down-times, longer opticslifetimes, better apparatus performance and improved devices that aremanufactured on the above-described apparatus. At least the reticle maybe used in the sealing of the projection beam aperture of the separator,which may lead to a significant reduction of contamination of the firstvacuum environment. Particularly, in this way, relatively low levels ofwater and hydrocarbon may be achieved in the first vacuum environment,thus preventing contamination of the projection system.

According to an aspect of the invention, there is provided alithographic apparatus that includes a first vacuum chamber and a secondvacuum chamber which is separated from the first vacuum chamber. Thefirst vacuum chamber includes a projection system for projecting apatterned beam onto a target portion of a substrate. The second vacuumchamber includes a support for supporting and moving a patterning devicein sight of the projection system.

According to an aspect of the invention, there is provided the use ofthe apparatus described above in the manufacturing of devices.

According to an aspect of the invention, there is provided the use of anapparatus described above in the manufacturing of devices, in which thepatterning device is scanned between at least a first and a secondposition for imparting a pattern to the radiation beam.

According to an aspect of the invention, there is provided a devicemanufacturing method that includes projecting a patterned beam ofradiation onto a substrate. A first vacuum environment that contains aprojection system is kept at a certain first pressure. A second vacuumenvironment that contains a support for supporting a patterning deviceis kept at a certain second pressure. The patterning device is held atleast partially near an aperture that extends between the first andsecond vacuum environment, for sealing that aperture. This may also leadto the above-mentioned advantages.

According to an aspect of the invention, a device manufacturing methodis provided. The method includes patterning a beam of radiation with apatterning device, and projecting the patterned beam of radiation onto asubstrate with a projection system. A first vacuum chamber that containsthe projection system is separated from a second vacuum chamber thatcontains a support for the patterning device. The beam of radiation istransmitted via at least one aperture from the first vacuum chamber tothe patterning device, and from the patterning device to the firstvacuum chamber, and at least one aperture is substantially sealed by aseal.

According to an aspect of the invention, in a device manufacturingmethod, a first vacuum chamber that contains a projection system isseparated from a second vacuum chamber that contains a support for apatterning device. A projection beam is transmitted via at least oneaperture from the first vacuum chamber to the patterning device, andfrom the patterning device to the first vacuum chamber and projected bythe projection system onto a substrate. The aperture is substantiallysealed by a seal.

According to an aspect of the invention, a device manufacturing methodusing a lithographic apparatus includes patterning a beam of radiationwith a patterning device, and projecting the patterned beam of radiationonto a target portion of a substrate with a projection system. A firstpart of the apparatus that includes at least part of the projectionsystem is disposed in a first vacuum environment. A second part of theapparatus is disposed in a second vacuum environment, and at least partof a surface of the patterning device is used for sealing an aperturethat extends between the first vacuum environment and the second vacuumenvironment.

According to an aspect of the invention, a device manufacturing methodincludes: providing a substrate; providing a projection beam ofradiation using an illumination system; using a patterning device toimpart the projection beam with a pattern in its cross-section; andprojecting the patterned beam of radiation onto a target portion of thesubstrate. At least a first part of the apparatus that includes part ofthe projection system is disposed in a first vacuum environment. Atleast a second part of the apparatus is disposed in a second vacuumenvironment. At least part of a surface of the patterning device is usedfor sealing an aperture that extends between the first vacuumenvironment and the second vacuum environment.

According to an aspect of the invention, there is provided a devicemanufactured using the apparatus described above and/or according to themethod described above.

According to an aspect of the invention, a computer, computer programand/or computer program product, arranged for controlling a lithographicapparatus to carry out a device manufacturing method is provided.

According to an aspect of the invention, a computer readable medium isprovided. The medium is encoded with a sequence of programmedinstructions which when executed by a processor are operable to cause alithographic apparatus to pattern a beam of radiation with a patterningdevice; and project the patterned beam of radiation onto a targetportion of a substrate with a projection system. A first part of theapparatus that includes at least part of the projection system isdisposed in a first vacuum environment. A second part of the apparatusis disposed in a second vacuum environment, and at least part of asurface of the patterning device is used for sealing an aperture thatextends between the first vacuum environment and the second vacuumenvironment.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 schematically depicts pressure zones of a lithographic apparatus;

FIG. 3 schematically depicts pressure zones of the lithographicapparatus of FIG. 1;

FIG. 4 depicts a cross-section of the apparatus according to theembodiment of FIG. 3, showing the sealing of the first vacuumenvironment from the second vacuum environment, wherein the reticle isin a first scan position;

FIG. 5 depicts a cross-section of the apparatus according to theembodiment of FIG. 3, showing the sealing of the first vacuumenvironment from the second vacuum environment, wherein the reticle isin a second scan position;

FIG. 6 a detail of a further embodiment of a lithographic apparatus, incross-section, wherein the apparatus also includes rema-blades;

FIG. 7 a detail Q of FIG. 6; and

FIG. 8 is a bottom view of the REMA blade section of FIG. 6.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus includes: an illuminationsystem (illuminator) IL configured to condition a radiation beam B (e.g.UV radiation or EUV radiation); a support structure (e.g. a mask table)MT constructed to support a patterning device (e.g. a mask) MA andconnected to a first positioner PM configured to accurately position thepatterning device in accordance with certain parameters; a substratetable (e.g. a wafer table) WT constructed to hold a substrate (e.g. aresist-coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate in accordance withcertain parameters; and a projection system (e.g. a refractiveprojection lens system) PS configured to project a pattern imparted tothe radiation beam B by patterning device MA onto a target portion C(e.g. comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as, for example, whether or notthe patterning device is held in a vacuum environment. The supportstructure can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure may be aframe or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” as used herein should be broadlyinterpreted as referring to any device that can be used to impart aradiation beam with a pattern in its cross-section such as to create apattern in a target portion of the substrate. It should be noted thatthe pattern imparted to the radiation beam may not exactly correspond tothe desired pattern in the target portion of the substrate, for example,if the pattern includes phase-shifting features or so-called assistfeatures. Generally, the pattern imparted to the radiation beam willcorrespond to a particular functional layer in a device being created inthe target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” as used herein should be broadlyinterpreted as encompassing any type of projection system, includingrefractive, reflective, catadioptric, magnetic, electromagnetic andelectrostatic optical systems, or any combination thereof, asappropriate for the exposure radiation being used, or for other factorssuch as the use of an immersion liquid or the use of a vacuum. Any useof the term “projection lens” herein may be considered as synonymouswith the more general term “projection system”.

As here depicted, the apparatus is of a reflective type (e.g. employinga reflective mask). Alternatively, the apparatus may be of atransmissive type (e.g. employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDincluding, for example, suitable directing mirrors and/or a beamexpander. In other cases, the source may be an integral part of thelithographic apparatus, for example, when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD, if required, may be referred to as a radiation system.

The illuminator IL may include an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as s-outer ands-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL mayinclude various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF2 (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam B. Similarly, the first positioner PMand another position sensor IF1 can be used to accurately position themask MA with respect to the path of the radiation beam B, e.g. aftermechanical retrieval from a mask library, or during a scan. In general,movement of the mask table MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of the substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner) themask table MT may be connected to a short-stroke actuator only, or maybe fixed. Mask MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks). Similarly, in situations inwhich more than one die is provided on the mask MA, the mask alignmentmarks may be located between the dies.

The depicted apparatus may be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PS. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIG. 2 shows a diagram of a lithographic apparatus, that includes areticle zone 102, a projection optics zone 101 and a wafer zone 199.

The optics zone 101 includes the projection optics system PS, as well asthe illuminator IL. The wafer zone 199 includes the wafer stage WS and awafer handler WH for transporting the wafers W.

The reticle zone 102 includes a reticle handler RH, a reticle supportstructure MT, a reticle stage actuator module MT-ACT, Rema-blades REBand a reticle stage metrology frame RS-MF. The first positioner PM,which includes both the reticle stage short stroke and long strokemodule, is, for example, an integral part of the reticle supportstructure MT and the reticle actuator module MT-ACT. The reticle handlerRH serves to transport reticles MA into and out of the apparatus.Positioning sensors IFI of a reticle stage measurement system areprovided in the reticle zone 102.

The reticle support structure is arranged to scan the reticle MA atleast over a desired distance in Y directions with respect to the opticsthat are located in the optics zone 101. Herein, movement of the masktable MT is realized with the aid of the long-stroke module (coarsepositioning) and the short-stroke module (fine positioning) of the firstpositioner PM. The long stroke module may provide movement in theY-direction only, whereas the short stroke module may providepositioning in 6 degrees of freedom.

The rema blades REB serve to limit the width of the size of the exposuredimensions. The construction and functioning of such blades REB isgenerally known in the field of lithography.

Additional and/or other optic functionalities may be placed between thereticle MA and the projection optics PS, if desired.

Inside the reticle zone 102, a Rema blade actuation module RE-ACT isprovided. This actuation module serves to control the position of theRema blades REB for providing a desired scan slit of the exposure field.

The reticle stage metrology frame RS-MF is also located within thereticle zone 102. As is shown in FIG. 2, this metrology frame RS-MF isarranged for allowing the projection beam PB to pass from theilluminator IL to the reticle MA, and from the reticle MA to theprojection system PS.

As is shown by light shading in FIG. 2, the reticle zone 102 and opticszone 101 are in the same vacuum environment, having a relatively lowpressure during use. Both the reticle zone 102 and optics zone 101 alsohave about the same partial pressures of water vapor and hydrocarbon.One or more vacuum pumps V1, V2 are provided for pumping the optics zone101 and reticle zone 102 down to a certain vacuum level, and formaintaining the vacuum therein.

The wafer zone 199 may (as source) have a higher partial vacuum regimethan the illuminator/optics for water and hydrocarbons, which is shownby a darker shading.

The functioning of the apparatus of FIG. 2 is substantially the same asthe above-described functioning concerning the apparatus of FIG. 1. Adisadvantage of the apparatus of FIG. 2 is that the low pressure region,which includes the reticle zone 102 and the optics zone 101, isrelatively large, which makes it relatively difficult and time-consumingto pump this region down to a desired vacuum level. Particularly, ittakes a relatively large effort to remove water and/or hydrocarbons fromthe optics zone 101, while large pump capacity is needed of a largeoutgassing contributing from the reticle zone compartment 102.

FIG. 3 schematically shows an apparatus according to an embodiment ofthe present invention. FIGS. 4 and 5 show part of this embodiment inmore detail. The apparatus of FIGS. 3-5 includes a first vacuum chamber11 for providing a first vacuum environment 1 with a first pressureduring use. The first chamber 11 contains an illumination system IL aswell as a projection system. The illumination system IL is configured tocondition a radiation beam, and the projection system is configured toproject a patterned radiation beam PB onto a target portion of asubstrate W. A second vacuum chamber 12 that has a second vacuumenvironment 2 with a second pressure during use is also provided. Thesecond chamber 12 contains a reticle support constructed to support thereticle MA, the reticle MA being capable of imparting a radiation beamwith a pattern in its cross-section to form the patterned radiationbeam, and a separator construction (or separator) 3 separating the firstvacuum environment 1 and the second vacuum environment 2. The separatorconstruction 3 includes a projection beam aperture 4 for passing theprojection beam PB from the first vacuum environment 1 towards thepatterning device MA and vice-versa.

In FIG. 3, the reference sign PS denotes the location of the projectionsystem. The separator construction 3 may be arranged and formed invarious ways. In the present embodiment, the reticle stage metrologyframe RS-MF is arranged for providing at least part of the separatorconstruction 3.

Similar to the apparatus of FIG. 1, the present embodiment of FIGS. 3-5further includes a substrate handler WH, as well as a substrate table-ina wafer stage WS—which is constructed to hold the substrate W. Theapparatus may also include a computer, computer program, or computerprogram product, arranged for controlling the lithographic apparatus.Such a controller is schematically depicted in FIGS. 4 and 5 by a boxwith reference sign CON.

As is shown in FIGS. 4 and 5, one or more first vacuum pumps V1 areprovided for realizing the first pressure of the first vacuumenvironment 1. One or more second vacuum pumps V2 are provided forrealizing the second pressure of the second vacuum environment 2. Thevacuum pumps V1, V2 as such are known to the skilled person, and may becoupled to the apparatus in various ways.

FIGS. 4 and 5 show two different positions of the reticle MA,respectively. The reticle support MT is arranged for moving thepatterning device MA at least over a certain distance in a direction Y.To this aim, the reticle support MT is movable over the distance by thefirst positioner PM. The distance is, for example, in the range of0.0-0.4 m, depending—amongst others—on the size of the reticle MA. Also,as follows from FIGS. 3-7, the reticle support MT is arranged forsupporting and moving the reticle MA such that the reticle MA is scannedin sight of the projection system of the projection system PS duringuse.

The separator construction 3 can be arranged in various ways, and mayinclude, for example, a suitable separation wall extending between thevacuum chambers, or the like. The projection beam aperture 4 extendsthrough the separator construction 3, in sight of the reticle MA. In thepresent embodiment, this aperture 4 has a tapered cross-section.Alternatively, the apparatus may include more than one projection beamaperture 4.

The outer perimeter of the separator construction 3 is sealed from anenclosure 7 of the apparatus by seal assemblies 6. These seal assemblies6 may be constructed in various ways, for example, the same as orsimilar to the seal assemblies described in U.S. Pat. No. 6,333,775,providing gas limiting seals between the first vacuum environment 1 andthe second vacuum environment 2 at the respective locations.

In the present embodiment, the reticle MA forms at least part of asealing construction (or seal) for substantially sealing the projectionbeam aperture 4 of the separator construction 3. As follows from FIGS. 4and 5, in each scanning position, the reticle MA forms part of thesealing arrangement for substantially sealing the projection beamaperture 4 of the separator construction 3. More particularly, thereticle MA and the separator construction 3 are arranged to cooperatefor providing a suitable seal of the aperture 4, particularly forpreventing or reducing transmission of water and/or hydrocarboncontamination to the first vacuum environment 1. Therefore, the reticleMA is conveniently used for substantially sealing that aperture 4, sothat contamination of the second vacuum environment and the reticle MAmay be prevented. Thus, the first vacuum environment 1 may be pumped torelatively low pressures, particularly concerning water and/orhydrocarbon concentrations, with relative ease and in relatively shortperiods of time.

As is clearly visible in FIGS. 4 and 5, in the present embodiment, thereticle support MT is arranged to hold the reticle MA at a certain smalldistance from the separator construction 3 for sealing the aperture 4thereof. This small distance is, for example, no more than about 1 mm,for sealing the aperture thereof. Preferable, the distance is no morethan about 0.3 mm.

Furthermore, the reticle support MT and the separator construction 3 arealso arranged to cooperate for the sealing of the aperture 4. Thus, inthe present embodiment, the support of the reticle MA may also form partof the sealing construction for substantially sealing the aperture 4 ofthe separator construction 3. Particularly, the reticle supportstructure MT includes a sealing part 8 which is located at a certainsmall distance opposite a sealing part 9 of the separator construction3. For example, the sealing part 8 of the reticle support structure MTextends at a distance of no more than about 1 mm from the sealing part 9of the separator construction 3, measured in a transversal direction Z,for sealing the aperture thereof. The smallest transversal distancebetween the sealing parts 8, 9 is preferably no more than about 1 mm.The reticle MA is being held within an enclosure of the sealing part 8of the reticle support structure MT. The sealing part 9 of the separatorconstruction 3 surrounds the projection beam aperture 4 in the virtualX-Y plane, which plane is perpendicular to the transversal Z-directionand parallel to the reticle MA.

Because of the small distances between the reticle support structure MTand the reticle MA on one hand and the separator construction 3 on theother hand, relatively small slits 5 separate the first vacuumenvironment 1 from the second vacuum environment 2, as viewed from upperend of the projection beam aperture 4 of the separator construction 3.These small slits 5 are also gas conduction limiting seals. They mayprovide the advantage that the reticle MA may be held in vibrationalisolation from the reticle stage metrology frame RS-MF, such that thereticle MA still assists in the sealing of the first vacuum environment1 from the second vacuum environment 2.

In an embodiment, the apparatus also includes blades REB for controllingthe dimensions of the projection beam PB. As shown in FIGS. 6 and 7,such blades REB extend at least partially between the patterning deviceMA and the aperture 4 of the separator construction 3 during use.Preferable, the blades REB also provide at least part of the sealing ofthe aperture 4 of the separator construction 3, so that these blades REBare used as sealing members as well.

FIGS. 6 and 7 schematically shows X-Rema-blades REB-X and Y-Rema-bladesREB-Y which are located near the reticle MA for controlling the shape ofthe projection beam in a X and Y directions, respectively. In thepresent embodiment, the Y-blades REB-Y are positioned nearer to thereticle MA than the X-blades REB-X, when viewed in the Z-direction.

For providing a sealing arrangement, the X-blades REB-X are located at asmall distance 10 a from the sealing part 9 of the separatorconstruction 3, measured in the Z-direction. This last-mentioneddistance is preferably not more than about 1 mm, and more preferably notmore than about 0.3 mm.

Also, the Y-blades REB-Y are located at small distances 10 b from thereticle MA and the sealing part 8 of the reticle support structure MT,for at least partially sealing the aperture 4 of the separatorconstruction 3 at the respective location. The last-mentioned distanceis also preferably no more than about 1 mm, and more preferably no morethan about 0.3 mm, measured in the Z-direction.

The smallest distance 10 c between the X-blades and Y-blades ispreferably less than about 1 mm, and more preferably less than about 0.3mm, when measured in the Z-direction.

The Rema blades, which are at the same level, may have the blades in onelevel, leading to a horizontal X-Y gap.

Following from the above, the embodiments of FIGS. 3-7 each include oneor more small gaps 5, 10 extending between the reticle MA and theseparator construction 3. In the present embodiments, the one or moresmall gaps extend substantially parallel to the reticle MA, betweensurfaces of the reticle MA, the opposite separator construction 3 andthe optional Rema blades REB. Preferably, the size of each of the gapsis sufficiently small for limiting the flow of water and/or hydrocarbonfrom an outer side of the gap. The outer side of the gap joins thesecond vacuum environment 2, towards an inner side of the gap, whichjoins the aperture 4 of the separator construction. Such a gap providesgood vibration isolation of the reticle stage, and also provides a goodseal between the first and second vacuum chambers 11, 12, particularlyconcerning water and/or hydrocarbon contamination.

In the present embodiment, the reticle support structure MT is locatedsubstantially in the second vacuum environment 2. Therefore, the reticlesupport structure MT is located outside the optics zone 1, so that anycontamination arising from the reticle support structure MT may beprevented from reaching the projection system PS relatively well. Also,in the present embodiment, the reticle positioner PM, including thereticle stage actuation module MT-ACT, is located substantially in thesecond vacuum environment 2. As shown in FIG. 3, the reticle handlingsystem RH for handling the reticle MA is preferably located in thesecond vacuum environment 2 as well. This further reduces the volume tobe pumped down to the low, first pressure, leading to shorter pumpingtimes concerning the removal of water vapor and/or hydrocarbon from thefirst vacuum chamber 11 and/or lower vacuum levels. To this aim, thepositioning sensors of the reticle stage measurement system, as shown inby reference sign IF1, may be provided in the second vacuum environment2.

The sealing construction is preferably arranged such, that a gasconductance from the second vacuum environment 2 via the projection beamaperture 4 to the first vacuum environment 1 is lower than about 100L/s. For example, the sealing construction can simply be arranged suchthat the mentioned gas conductance via the projection beam aperture 4 islower than about 20 L/s. Therefore, the first vacuum environment 1 maybe maintained at a desired low pressure, and relatively free fromcontamination. For example, and as a non-limiting example, theconductance for water at 22° C. can be only about 9.3 L/s when thesealing gap has a height of about 1 mm, a length of about 23 mm, and awidth of about 416 mm.

The first and/or second vacuum environment may contain at least oneinert gas, for example, helium, argon and/or the-like, that is the maincontributor to the total pressure of the first and/or second vacuumenvironment. The partial pressures of water vapor and hydrocarbon arepreferably much lower than the total pressure, for preventingcontamination of the first vacuum environment 1.

As follows from above, the sealing construction preferably leads torelatively low partial pressures of hydrocarbon and water in the firstvacuum chamber 12. Preferably, the partial pressure of water and/orhydrocarbon in the first vacuum environment 1 is at least about 100times lower than the partial pressure of water and/or hydrocarbon in thesecond vacuum environment 2.

For example, the partial pressure of water in the second vacuumenvironment 2 may be about 10⁻⁵ mbar or smaller, during use. The partialpressure of water in the second vacuum environment 2 may be, forexample, in the range of about 10⁻⁵-10⁻⁷ mbar Also, the partial pressureof hydrocarbon in the second vacuum environment 2 may be about 10⁻⁷ mbaror smaller. For example, the partial pressure of hydrocarbon in thesecond vacuum environment 2 may in the range of about 10⁻⁷ 10⁻⁹ mbar.Then, the sealing arrangement may be arranged such that the partialpressure of water in the first vacuum environment 1 is about 10⁻⁷ mbaror smaller, whereas the partial pressure of hydrocarbon in the firstvacuum environment 1 is about 10⁻⁹ mbar or smaller.

In one embodiment, the total pressure in the first vacuum environment 1is about the same as the total pressure in the second vacuum environment2. Thus, the occurrence of relatively high gas flows from the second tothe first vacuum chamber may be prevented in a simple manner. Forexample, the total pressure of the second vacuum environment 2 may be inthe range of about ½ to 1½ times the pressure of the first vacuumenvironment 1. This range may also be smaller, for example, about plusor minus 10% of the pressure of the first vacuum environment 1.

In an embodiment, the first vacuum environment 1 may have a lower totalpressure than the second vacuum environment 2. For example, the firstvacuum environment 1 may have a total pressure which is at least 1.5 andpreferably minimally 10 times less than the total pressure of the secondvacuum environment 2. By applying such a pressure difference,contamination of the optics in the first vacuum chamber 11 can beprevented well. In this way, vacuum requirements and the respectivevacuum construction of the second vacuum chamber 12 may be lessstringent.

The total pressure of gas in the second vacuum chamber 12 may be, forexample, about 10⁻² mbar or smaller. Further, the total pressure of gasin the first vacuum chamber 12 may be, for example, about 10⁻⁵ mbar orsmaller.

Because of the above-described construction of the apparatus, theapparatus includes a movable seal for substantially sealing theprojection beam aperture 4. Herein, the patterning device MA is simplypart of the moving seal. The support for supporting the patterningdevice is also part of the moving seal. The moving seal may be movable,for example, over a distance in the range of 0-40 cm with respect to theseparator construction 3. The control blades REB for controlling thedimensions of the projection beam PB may also form part of the seal ofthe projection beam aperture 4.

During use of the apparatus according to the present invention, thereticle MA is scanned between at least a first and a second position forimparting a pattern to the radiation beam PB. Particularly, during use,the reticle MA is moved at least between a first and a second positionwith respect to the aperture 4 of the separator construction 3, forscanning the projection beam over the reticle MA. This use may involve adevice manufacturing method that includes projecting the patterned beamof radiation PB onto a substrate, wherein the first vacuum environment 1and second vacuum environment 2 are kept are respective pressures. Inthis method, the patterning device MA is held at close distance near theprojection beam aperture 4, simply for sealing that aperture 4.Preferably, the reticle MA is scanned along the upper end of theaperture 4, such that the reticle MA always covers the aperture 4 duringthe scanning process. Herein, the reticle MA is also held at a smalldistance from the separator construction 3. The sealing of theprojection beam aperture 4 is also achieved during use by the describedreticle support and by the optional control members REB for controllingthe dimensions of the projection beam PB. Particularly, during use, theaperture 4 is sealed by the one or more small, vibration isolation gapswhich extend between the reticle MA, the opposite separator construction3 and intermediate control members REB.

Various pressures may be used in the first and second vacuum chamber, ashas been mentioned above. Because of the sealing of the projection beamaperture 4, only small gas flows—if any—can reach that aperture 4 fromthe second vacuum environment 2. Such gas flows are depicted by arrows fin FIGS. 4 and 5. Small amount of gas may flow through the vibrationisolation sealing assemblies 6, as has been indicated by arrows g. Suchvibration isolation assemblies 6 can be sealed, for example, by foil,small gaps and the like. Thus, the first and second vacuum environments1, 2 are separated relatively well from each other. Preferably, thisseparation is such that the partial pressure of water in the firstvacuum environment 1 is about 10⁻⁷ mbar or smaller, whilst the partialpressure of hydrocarbon in the first vacuum environment 1 is about 10⁻⁹mbar or smaller. It is preferred to allow higher partial pressures ofthese gasses in the second chamber 2, for example, at least about 10times higher, than the partial pressures in the first chamber 1.

During use, the described operation of the apparatus may be at leastpartially controlled by the computer, computer program or computerprogram product. Such a controller CON may be arranged, for example, forcontrolling the positioning of the reticle MA with respect to theprojection beam aperture 4 for substantially sealing that aperture 4,and the-like.

Because of the above-described arrangement of the apparatus of thepresent invention, contamination of the projection system may beprevented relatively well, leading to lower system down-times, longeroptics lifetimes, better apparatus performance and improved devicesmanufactured thereby. Apparatus parts that do not have opticalfunctionality, for example, EUV optical functions, are preferably placedoutside the first vacuum environment 1, away from the optics of theprojection system. Therefore, any outgassing of such apparatus partswill not—or only in very small amounts—affect the optics of theapparatus. Also, the optics zone 1 may be pumped down to a desiredvacuum level relatively fast, and/or to lower vacuum pressure levels.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in, for example, atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example, imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography, atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus comprising: a support constructed to supporta patterning device, the patterning device being capable of imparting aradiation beam with a pattern in its cross-section to form a patternedradiation beam; a projection system configured to project the patternedradiation beam onto a target portion of a substrate; a first vacuumenvironment that contains said projection system; a second vacuumenvironment that contains said patterning device support; and aseparator that separates the first vacuum environment and the secondvacuum environment, the separator comprising an aperture for passingsaid projection beam from the first vacuum environment towards thepatterning device and/or vice-versa, wherein said patterning deviceforms at least part of a seal for substantially sealing the aperture ofthe separator.
 2. An apparatus according to claim 1, wherein the supportis arranged to hold the patterning device at a certain small distancefrom the separator for sealing said aperture thereof.
 3. An apparatusaccording to claim 2, wherein the support is arranged to hold thepatterning device at a distance of no more than about 1 mm from theseparator for sealing said aperture thereof.
 4. An apparatus accordingto claim 1, wherein the support forms at least part of the seal forsubstantially sealing the aperture of the separator.
 5. An apparatusaccording to claim 4, wherein the support comprises a sealing part whichis located at a certain small distance from a sealing part of theseparator.
 6. An apparatus according to claim 5, wherein the distance isno more than about 1 mm.
 7. An apparatus according to claim 1, whereinblades for controlling the dimensions of said projection beam extend atleast partially between said patterning device and the aperture of theseparator, wherein said blades provide at least part of the sealing forsubstantially sealing the aperture of the separator.
 8. An apparatusaccording to claim 7, wherein at least one of said blades is located ata small distance from a sealing part of the separator for at leastpartially sealing the aperture of the separator.
 9. An apparatusaccording to claim 8, wherein at least one of said blades is located ata small distance of not more than about 1 mm from the sealing part ofthe separator.
 10. An apparatus according to claim 7, wherein at leastone of said blades is located at a small distance from the patterningdevice and/or the support for at least partially sealing the aperture ofthe separator.
 11. An apparatus according to claim 10, wherein thedistance is no more than about 1 mm.
 12. An apparatus according to claim1, wherein at least one small gap extends between said patterning deviceand said separator, wherein the size of said gap is sufficiently smallfor limiting the gas conductance of water and/or hydrocarbon from anouter side of the gap, said outer side joining the second vacuumenvironment towards an inner side of the gap, said inner side joiningthe aperture of the separator.
 13. An apparatus according to claim 1,wherein said patterning device and said separator are arranged tocooperate for substantially sealing said aperture of said separator. 14.An apparatus according to claim 1, wherein said support and saidseparator are arranged to cooperate for substantially sealing saidaperture of said separator.
 15. An apparatus according to claim 1,wherein, during use, the patterning device moves at least between afirst and a second position with respect to the aperture of theseparator for scanning the projection beam over the patterning device.16. An apparatus according to claim 1, wherein the support is arrangedfor moving the patterning device over a relatively short distance in acertain direction, wherein said relatively short distance is in therange of 0-0.4 m.
 17. An apparatus according to claim 16, wherein saidsupport, and a positioner thereof, are located substantially in saidsecond vacuum environment.
 18. An apparatus according to claim 1,wherein at least a reticle stage actuation module that is arranged formoving the patterning device over a relatively long distance in acertain direction is located substantially in said second vacuumenvironment.
 19. An apparatus according to claim 1, wherein said seal isarranged such that a conductance from the second vacuum environment tothe first vacuum environment is lower than about 100 L/s, and whereinsaid conductance is the conductance of water and/or hydrocarbons.
 20. Anapparatus according to claim 1, wherein said seal is arranged such thata conductance from the second vacuum environment to the first vacuumenvironment is lower than about 20 L/s, and wherein said conductance isthe conductance of water and/or hydrocarbons.
 21. An apparatus accordingto claim 1, wherein at least part of said seal moves with respect to theseparator during use.
 22. An apparatus according to claim 21, whereinthe moving part of said seal is movable over a distance in the range of0-40 cm with respect to the separator during use.
 23. An apparatusaccording to claim 1, wherein a reticle handling system for handling thereticle is located at least partially in the second vacuum environment.24. An apparatus according to claim 1, wherein the partial pressure ofwater vapor in the second vacuum environment is about 10⁻⁵ mbar orsmaller, and/or wherein the partial pressure of hydrocarbon in thesecond vacuum environment is about 10⁻⁷ mbar or smaller.
 25. Anapparatus according to claim 24, wherein the total pressure in thesecond vacuum environment is about 10⁻² mbar or smaller.
 26. Anapparatus according to claim 1, wherein the total pressure in the firstvacuum environment is about the same as the total pressure in the secondvacuum environment, and wherein said total pressure is preferably about10⁻² mbar or smaller.
 27. An apparatus according to claim 1, wherein thepartial pressure of water vapor in the first vacuum environment is about10⁻⁷ mbar or smaller, and/or wherein the partial pressure of hydrocarbonin the first vacuum environment is about 10⁻⁹ mbar or smaller.
 28. Anapparatus according to claim 27, wherein the total pressure in the firstvacuum environment is about 10⁻⁵ mbar or smaller.
 29. An apparatusaccording to claim 1, further comprising an illumination systemconfigured to condition the radiation beam.
 30. An apparatus accordingto claim 1, further comprising a substrate table constructed to hold thesubstrate.
 31. A lithographic apparatus comprising a first vacuumchamber, and a second vacuum chamber which is separated from said firstvacuum chamber by a separator, wherein the first vacuum chambercomprises a projection system for projecting a patterned beam ofradiation onto a target portion of a substrate, and wherein the secondvacuum chamber comprises a support for supporting and moving apatterning device in sight of the projection system.
 32. An apparatusaccording to claim 31, further comprising an aperture extending betweenthe first vacuum chamber and the second vacuum chamber for transmittingthe projection beam of radiation, wherein said aperture is sealed fromthe second vacuum chamber by one or more small gaps which extend inparallel with the patterning device.
 33. An apparatus according to claim32, wherein one or more of said small gaps extend between the patterningdevice and a surface of an opposite sealing member.
 34. An apparatusaccording to claim 33, wherein said sealing member is at least oneblade, said blade being constructed for controlling the dimensions ofsaid projection beam of radiation.
 35. An apparatus according to claim33, wherein said sealing member is at least part of a separation wallextending between said vacuum chambers.
 36. An apparatus according toclaim 32, wherein one or more of said small gaps extend between at leastone blade, said blade being arranged for controlling the dimensions ofsaid projection beam of radiation, and at least part of a separationwall extends between said vacuum chambers.
 37. An apparatus according toclaim 32, wherein one or more of said small sealing gaps extend betweenat least two of said blades, wherein a smallest distance between theblades is about 1 mm or less.
 38. An apparatus according to claim 31,wherein the support is arranged to move the patterning device over adistance in the range of 0-40 cm with respect to the separator duringuse.
 39. An apparatus according to claim 31, wherein the second vacuumchamber also comprises a first positioner for moving the patterningdevice in one or more directions, wherein the first positioner comprisesa long stroke module and a short stroke module, a reticle handlingsystem for handling the reticle, and/or a positioning sensor of areticle stage measurement system.
 40. A lithographic projectionapparatus arranged to project a pattern from a patterning device onto asubstrate, the apparatus comprising a first vacuum chamber, a secondvacuum chamber, and a moving seal for substantially sealing an aperturewhich extends between the first vacuum chamber and the second vacuumchamber in sight of the patterning device.
 41. An apparatus according toclaim 40, wherein the patterning device is part of the moving seal. 42.An apparatus according to claim 40, wherein a support for supporting thepatterning device is part of the moving seal.
 43. An apparatus accordingto claim 41, wherein control members for controlling the dimensions ofsaid projection beam are part of the seal of said aperture.
 44. A devicemanufacturing method comprising projecting a patterned beam of radiationonto a substrate, wherein a first vacuum environment, containing aprojection system, is held at a certain first pressure, wherein a secondvacuum environment, containing a support for supporting a patterningdevice, is held at a certain second pressure, wherein said patterningdevice is held at least partially near an aperture extending between thefirst and second vacuum environment for sealing the aperture.
 45. Amethod according to claim 44, wherein the patterning device is scannedalong said aperture such that the patterning device always covers theaperture during the scanning.
 46. A method according to claim 45,wherein the patterning device is held at a small distance from aseparator that separates the first vacuum environment and the secondvacuum environment, said separator comprising said aperture.
 47. Amethod according to claim 44, wherein the partial pressure of watervapor in the second vacuum environment is about 10⁻⁵ mbar or smaller.48. A method according to claim 44, wherein the partial pressure ofhydrocarbon in the second vacuum environment is about 10⁻⁷ mbar orsmaller.
 49. A method according to claim 44, wherein the total pressurein the first vacuum environment is about the same as the total pressurein the second vacuum environment, wherein said total pressure preferablyis about 10⁻² mbar or smaller.
 50. A method according to claim 44,wherein the partial pressure of water vapor in the first vacuumenvironment is about 10⁻⁷ mbar or smaller.
 51. A method according toclaim 44, wherein the partial pressure of hydrocarbon in the firstvacuum environment is about 10⁻⁹ mbar or smaller.
 52. A devicemanufacturing method comprising: patterning a beam of radiation with apatterning device; and projecting the patterned beam of radiation onto asubstrate with a projection system, wherein a first vacuum chamber thatcontains the projection system is separated from a second vacuum chamberthat contains a support for the patterning device, wherein the beam ofradiation is transmitted via at least one aperture from the first vacuumchamber to the patterning device, and from the patterning device to thefirst vacuum chamber, and wherein said at least one aperture issubstantially sealed by a seal.
 53. A method according to claim 52,wherein the patterning device is scanned with respect to said at leastone aperture.
 54. A method according to claim 53, wherein the patterningdevice is used as part of the seal for sealing said aperture.
 55. Amethod according to claim 54, wherein the support is used as part of theseal for sealing said aperture.
 56. A method according to claim 54,wherein control members for controlling the dimensions of saidprojection beam are used in sealing said aperture.
 57. A methodaccording to claim 52, wherein said aperture is being sealed by one ormore small, vibration isolation gaps.
 58. A device manufacturing methodusing a lithographic apparatus, the method comprising: patterning a beamof radiation with a patterning device; and projecting the patterned beamof radiation onto a target portion of a substrate with a projectionsystem, wherein a first part of the apparatus that comprises at leastpart of said projection system is disposed in a first vacuumenvironment, wherein a second part of said apparatus is disposed in asecond vacuum environment, and wherein at least part of a surface of thepatterning device is used for sealing an aperture extending between thefirst vacuum environment and the second vacuum environment.
 59. A methodaccording to claim 58, wherein the first vacuum environment and secondvacuum environment have substantially the same total pressure, whereinthe partial pressure of water and/or hydrocarbon in the first vacuumenvironment is at least about 10 times lower than the partial pressureof water and/or hydrocarbon in the second vacuum environment.
 60. Amethod according to claim 58, wherein the first vacuum environment has alower total pressure than the second vacuum environment, wherein thepartial pressure of water and/or hydrocarbon in the first vacuumenvironment is at least about 10 times lower than the partial pressureof water and/or hydrocarbon in the second vacuum environment.
 61. Amethod according to claim 44, wherein the total pressure in the firstvacuum environment is about 10⁻⁵ mbar or smaller.
 62. A method accordingto claim 44, wherein the total pressure in the second vacuum environmentis about 10⁻² mbar or smaller.
 63. A device manufactured according tothe method of claim
 44. 64. A computer readable medium encoded with asequence of programmed instructions which when executed by a processorare operable to: pattern a beam of radiation with a patterning device;and project the patterned beam of radiation onto a target portion of asubstrate with a projection system, wherein a first part of theapparatus that comprises at least part of said projection system isdisposed in a first vacuum environment, wherein a second part of saidapparatus is disposed in a second vacuum environment, and wherein atleast part of a surface of the patterning device is used for sealing anaperture extending between the first vacuum environment and the secondvacuum environment.